The present invention relates to a windshield wiping device for cleaning motor vehicle windshields.
Windshield wiping devices for cleaning motor vehicle windshields are conventional. Conventional devices of this type usually have two switch positions for different wiper speeds, as well as a position for intermittent operation. Depending on the degree to which the windshield is wetted, the wiper arm moving over the windshield, due to frictional forces, experiences different levels of resistance. The frictional forces operating on the rubber lips of the wiper are the smallest at the second, more rapid velocity level, and on a wet windshield. The geometric design of the windshield wiping device, with respect to the maximum possible wiping field, must therefore take this operating state into account.
On the other hand, at the usually roughly 30% slower first velocity level, the result, in the turning points, is a smaller wiping field, and therefore also a smaller vision field, because the momentum of the wiping device, as a result of the moments of inertia of the moving parts, and particularly so on a dry windshield, is significantly less than on a wet windshield at the rapid level. A corresponding enlargement of the wiping field at the first level, at the second level on a wet windshield, would lead to a deflection of the windshield wiper beyond the windshield and therefore to faulty functioning or damage to the wiper.
To render the end positions of the wiper arms as congruent as possible at the two velocity levels, there are conventional measures, shortly before the wiper arm reaches the upper or the lower end position, to switch the electrical drive motor of the windshield wiping device to the slower velocity level and, as a result, to maintain the inertial forces, and thus the lag of the windshield wiping device, at as constant a value as possible.
Thus, WO PCT Publications No. 96/09944 describes a windshield wiping device having a supplemental switching device, which, shortly before the turning points, switches from a more rapid velocity level to a slower level. For this purpose, an electrical switch is mechanically coupled to the rotor of the electrical drive motor. The switch has a plurality of concentric cams for the periodic control of contact tags. Disadvantageous in the system is the relatively complex and bulky design of the switch, which, in addition, cannot be realized using conventional switches as they are usually employed in motor vehicles. Also, no provision is made for an integrated control of a park position.
The windshield wiping device according to the present invention has the particular advantage, as a result of simple mechanical components, of achieving a maximum possible wiping field on the windshield of a motor vehicle. This is essentially achieved as a result of the fact that at the second velocity level, which is higher than a first velocity level of the electrical drive motor of the windshield wiping device, shortly before the at least one wiper arrives at the upper or the lower end position (the turnaround point), a switchover takes place to the first, i.e., slower velocity level, and, shortly after leaving the upper or lower end position, a return to the second velocity level is carried out. This switchover occurs in a simple manner through the use of a contact disk system rotating in concert with the motor revolutions. The contact disk system, for example, is able to periodically change the motor velocity through three contact tags sliding on partially interrupted pathways and acting as switching contacts. In the same manner, the precise resting position of the windshield wiper can also be assured in the lower end position after switchoff. For this purpose, it is advantageous to arrange two contact disk systems so as to be coaxial in relation to each other, so that a fixed assignment of the angle positions of the contact disks is made possible with regard to the position of the windshield wiper on the windshield.
It is particularly advantageous that the contact disk systems have a simple interface with regard to a steering column switch. The steering column switch has a very simple and proven design and function.
In an advantageous embodiment, the contact disk has connected to it not the entire engine voltage but rather a small control voltage, which can then drive a power transistor or thyristor.
Another advantageous embodiment of the present invention can provide for electronic detection of the wiper position, for example using a rotating perforated disk for driving a photo-electric reader or a Hall sensor. Its signals can be used by a downstream evaluating circuit for the precise maintenance of a maximum wiping field.